YZGD from Paenibacillus thiaminolyticus, a pyridoxal phosphatase of the HAD (haloacid dehalogenase) superfamily and a versatile member of the Nudix (nucleoside diphosphate x) hydrolase superfamily

摘要

pYZGD from iPaenibacillus thiaminolyticus/i is a novel bifunctional enzyme with both PLPase (pyridoxal phosphatase) and Nudix (nucleoside diphosphate x) hydrolase activities. The PLPase activity is catalysed by the HAD (haloacid dehalogenase) superfamily motif of the enzyme, and the Nudix hydrolase activity is catalysed by the conserved Nudix signature sequence within a separate portion of the enzyme, as confirmed by site-directed mutagenesis. YZGD9s phosphatase activity is very specific, with pyridoxal phosphate being the only natural substrate, while YZGD9s Nudix activity is just the opposite, with YZGD being the most versatile Nudix hydrolase characterized to date. YZGD9s Nudix substrates include the CDP-alcohols (CDP-ethanol, CDP-choline and CDP-glycerol), the ADP-coenzymes (NADH, NAD and FAD), ADP-sugars, TDP-glucose and, to a lesser extent, UDP- and GDP-sugars. Regardless of the Nudix substrate, one of the products is always a nucleoside monophosphate, suggesting a role in nucleotide salvage. Both the PLPase and Nudix hydrolase activities require a bivalent metal cation, but while PLPase activity is supported by Cosup2+/sup, Mgsup2+/sup, Znsup2+/sup and Mnsup2+/sup, the Nudix hydrolase activity is Mnsup2+/sup-specific. YZGD9s phosphatase activity is optimal at an acidic pH (pH 5), while YZGD9s Nudix activities are optimal at an alkaline pH (pH 8.5). YZGD is the first enzyme reported to be a member of both the HAD and Nudix hydrolase superfamilies, the first PLPase to be recognized as a member of the HAD superfamily and the first Nudix hydrolase capable of hydrolysing ADP-x, CDP-x and TDP-x substrates with comparable substrate specificity./p